Activity Introduction
Curriculum outcome
1a) S1-4-01 Use a coordinate system to locate visible celestial objects, and construct an
astrolabe to determine the position of these objects.
Include: Altitude, Azimuth
1b) The purpose of the activity is for students to learn to locate celestial objects in the
night sky and plot their location using the altitude-azimuth coordinate system. The
altitude-azimuth coordinate system consists of the altitude of an object in the sky, given
in degrees from zero to 90 (we will use the constructed astrolabe to find this), and the
compass direction of the object, given in degrees between zero and 360 (zero being due
north, 90 due east, 180 due south, and 270 due west).
1c) The justification for the approach I have taken is that celestial objects are more easily
viewed at night and since students do not attend school at night. It is justified that they
perform this activity on their own time when it can be done at night.
1d) It is important that the students understand what azimuth and altitude are before
starting this activity.
The Altitude of a celestial body is its angular distance above the Horizon.
The Azimuth of a celestial body is the bearing of the body from your position, as
measured clockwise from true North.
Class Procedure
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Begin the class by explaining what azimuth and altitude are and how they relate to
locating celestial objects.
Demonstrate to students how to find celestial objects azimuth using a compass. To
find azimuth you trace a line straight down from the object to the nearest horizon
point, and then read the bearing on your compass where that point hits. Remember
that 90۫۫۫۫۫ would be due east, 180۫ would be due south, 270۫ would be due
west, 0۫ or 360۫ would be due north. So if your object was 30۫ , you would write
your object as being 30۫ North, North, East or 30۫ NNE.
Work with students to construct astrolabes.
- materials needed:
- thick corrugated cardboard (about 8.5" x 11" or similar)
- scissors
- 20 cm of thin string or colored fishing line
- weight (washer, nut, or similar object that can be tied onto the string)
- large drinking straw (at least 0.5 cm in diameter)
- glue
- transparent tape
Demonstrate to students how to use their astrolabe to determine celestial objects
altitude. To find the altitude of the object you need to pinch the string with your
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free hand, against the scale on the astrolabe. Remember that 0۫ is your horizon
and 90۫ is straight above you.
Show students some examples of altitude and azimuth coordinates for a couple
celestial objects.
E.g)
Evening planets one hour after sunset (W to E):
Planet Altitude Azimuth
Uranus 20º
Mars
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60º
249º WSW
91º E
Hand out Locating Celestial Objects in the Night Sky assignment/activity and
explain to the students what is expected of them. Tell students that the assignment
is to be done on their own time, and recordings are to be taken two times a week
for the next three weeks. Tell students that recordings should be taken a minimum
of three days apart.
Go over the star chart procedure and field any questions on it.
Provide students with time to pick the objects they wish to view. Students are to
use this time to research their chosen objects to make certain that they are able to
be viewed from our location at this time of year.
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Locating Celestial Objects in the Night Sky
Objective: Using an astrolabe and a compass determine the altitude and azimuth of
celestial objects in the night sky.
Materials
Student constructed astrolabe
Compass for measuring azimuth
Observation Chart
Star Chart
Activity procedure:
The activity is to be done on students own time, recordings are to be taken twice weekly
for the next three weeks.
1) Select 3 to 5 objects in the night sky that you wish to locate. It is important to
check that the object you have chosen will be visible during the time you are
doing the activity. i.e.) some celestial objects or only visible during certain times
of the year. A possible objects that could be located are The Moon, Polaris (the
North Star), the stars Dubne and Merak, Venus, Mars, Jupiter etc. Students will be
provided with a star chart and directions on how to use it to locate stars in the sky.
2) Determine the azimuth of your selected objects using the compass. As you have
already learned azimuth is determined by visually tracing a line from the object
straight down to the nearest horizon point, and reading its compass bearing.
Record the bearing in your observation chart. Remember 90۫۫۫۫۫ would be due
east, 180۫ would be due south, 270۫ would be due west, 0۫ or 360۫ would be
due north.
3) Using the astrolabe, look through the straw until you can locate the object in the
field of view. To find the altitude of the object you need to pinch the string with
your free hand, against the scale on the astrolabe. Record the object’s altitude in
the observation chart. To increase the accuracy of your reading, perform this step
two or more times for each object.
4) Be prepared to discuss your results with a classmate or group on how you
determined your readings. It may be useful to arrange for you and another
classmate to observe the same objects at the same time, so that you can compare
results.
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Date and Time of
Observation
1st Observation
2nd Observation
3rd Observation
4th Observation
5th Observation
6th Observation
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Objects Viewed
Azimuth
(in degrees)
from compass
Altitude as
measured by
Astrolabe
Star Chart Procedure
1) Use your compass to make yourself face North.
2) Find the Meridian in the sky and on the star chart using the date.
3) Find the field of view on the star chart and compare the stars seen on the chart
with those in the sky.
The meridian is an imaginary curve that passes through the north horizon, the North Star
(Polaris), the point directly overhead (zenith) and the south horizon as shown below. Note
that Polaris is not the brightest star in the sky. You can use Dubhe and Merak of Ursa
Major as pointer stars to help you find Polaris.
The meridian on the star chart can be located using the date. The dates along the outer
edge of the chart represent the location of the meridian.
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SFA Star Chart" - Northern Region
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